RETENTION OF NUTRIENTS AND HEAVY-METALS IN MANGROVE SEDIMENT RECEIVING WASTE-WATER OF DIFFERENT STRENGTHS

Column leaching experiments were conducted to assess the retention of nutrients and heavy metals in mangrove sediments receiving wastewater of different strengths. The amounts of pollutants retained in the sediments increased with the strength of wastewater. The sediments leached with the strongest wastewater had the highest concentration of NH4+-N, NO3--N, P, Cu, Mn, Zn and Cd. Most of the retained wastewater-borne pollutants were concentrated in the first 4 cm of the sediment column, with very little downwards migration. This suggests that the mangrove sediments acted as an efficient trap for immobilization of nutrients (in particular P) and heavy metals.